1. Field of the Invention
The present invention relates to a braking system for an electric vehicle including driven wheels which are connected to and driven by a motor using a battery as an energy source and which are braked hydraulically and regeneratively on the basis of the operation of a brake operating element.
2. Description of the Prior Art
There are conventionally known electric vehicles having driven wheels capable of being braked hydraulically and regeneratively, which are described in Japanese Patent Publication No. 28933/74. In such electric vehicle, the recovery of energy by a regenerative braking can be preferentially performed to charge the battery as much as possible, and after the magnitude of a regenerative braking force reaches a limit, a hydraulic braking force can be additionally used to insure a sufficient braking force.
In order to preferentially exhibit the regenerative braking force, it is conceived that while the depression force on a brake pedal is small, the hydraulic braking pressure generated by a master cylinder may be cut by a differential pressure regulating valve so that it is not transmitted to a brake cylinder, and when the depression force on a brake pedal is increased, the hydraulic braking pressure generated by the master cylinder may be reduced by the differential pressure case, the differential pressure regulating valve has various input and output characteristics and hence, if the characteristic of the differential pressure regulating valve and the magnitude of the regenerative braking force do not suit to each other, the sum total of the hydraulic braking force and the regenerative braking force is not proportional to the quantity of brake pedal operated, and the feeling of braking may be degraded.
In a vehicle using an internal combustion engine as a drive source, in addition to a hydraulic braking force generated by the operation of the brake pedal, a so-called engine braking force can be applied by releasing the accelerator pedal. On the other hand, in an electric vehicle in which a motor functions as a power generator to exhibits a regenerative braking force, if the regenerative braking force is exhibited by the operation of the brake pedal, a braking force corresponding to an engine brake of the vehicle including the internal combustion engine as a drive source is not obtained, resulting in a degraded feeling of braking. In addition, if the regenerative braking force is controlled by the operation of the accelerator pedal, most of the kinetic energy of the vehicle is abandoned by the hydraulic braking, resulting in a poor economy.